This invention relates to electrodes and, more particularly, to ruthenium coated electrodes and a method for manufacturing such electrodes.
Electrodes, in general, are used in a variety of different processes such as electrolytic processes, electrowinning of metals, cathodic protection, etc. In an electrolytic process, such as for the production of halogen and alkali metal hydroxide, so-called low overvoltage electrodes are employed in electrolytic cells to reduce some of the large amounts of energy consumed during the cell's operation. It is well known to manufacture low overvoltage electrodes by coating an electroconductive substrate, such as titanium, nickel, iron, or steel, or with an electrolytically-active material, for example, a platinum group metal or oxides thereof, or alloys thereof. A "platinum group metal" refers to one of the metals of platinum, iridium, ruthenium, rhodium, osmium, palladium, or alloys thereof. Common coating methods used to produce low overvoltage electrodes are, for example, plasma or flame spraying, electrodeposition, and electroless or chemical deposition.
Low overvoltage electrodes, anodes or cathodes, are typically coated with a ruthenium metal surface by an electrodeposition method. For example, U.S. Pat. No. 3,578,572 describes a method for electroplating a platinum metal, such as ruthenium, onto a titanium support and using this platinum metal coated support as an electrode, particularly an anode, in aqueous alkali metal chloride electrolytes. Also, U.S. Pat. No. 3,974,058 specifically describes electroplating ruthenium on a metal substrate with an intermediate coating of cobalt for use as a cathode in electrolytic cells.
In the above methods, however, the ruthenium electroplating baths used to plate the metal on a substrate are acidic. In an acidic environment displacement plating may occur. Thus, many metallic substrates, such as copper, nickel, or steel, cannot be satisfactorily plated with ruthenium in acidic solutions without first applying a protective "flash" coating of a suitable metal, such as gold or other suitable metals to the substrate.
It is desired to provide a ruthenium coated electrode and method for making the electrode which reduces the displacement plating experienced using existing methods.